Optical sensing arrays employing misaligned squinted optical axes compared to aligned axes

• US 5,393,973 A
• Filed: 12/16/1993
• Issued: 02/28/1995
• Est. Priority Date: 12/16/1993
• Status: Expired due to Term

• Current Assignee: Scientific Technologies Incorporated
• Original Assignee: Scientific Technologies Incorporated
• Inventors: Blau, David
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): NICHOLS, STEVEN
• Application Number:
  US08/168,717
• Time in Patent Office: 439 Days
• Field of Search: 250/221, 250/222.1, 340/555, 340/556, 340/557
• US Class Current: 250/221
• CPC Class Codes: G01V 8/20 using multiple transmitters or receivers

Abstract

An optical sensing array and method of operation for controlling the acceptance angle of light beams which are iteratively strobed in side-by-side channels between light transmitters and light receivers. The light beams in at least a pair of channels are directed along axes which are intentionally mispointed or squinted. A control circuit measures the amplitudes of signals produced responsive to light being received by the light receivers and compares the ratio of those amplitudes to the ratio of predetermined high and low amplitude values which provide a threshold window. When the ratio of the signal amplitudes exceeds the ratio of the window threshold values, an output signal is produced indicative of an unsafe operating condition. The control circuit further maintains the gain of the signals from the light receivers to stay within the range of the predetermined window threshold values.

Claims

1. A method of operating an optical sensing array for controlling the acceptance angle of light beams which are iteratively strobed in cycles from a plurality of light transmitters in side-by-side channels toward a plurality of light receivers which are associated with respective channels and are adapted to sense the light beams for producing signals, the method comprising the steps of directing the light beam in a first one of the channels along a first axis which is squinted relative to a second axis along which the light beam in at least a second one of the channels is strobed, producing a signal V₁ responsive to light being sensed by the light receiver associated with the first channel, producing a signal V₂ responsive to light being sensed by the light receiver associated with the second channel, establishing a predetermined high amplitude value V_H, establishing a predetermined low amplitude value V_L which is below V_H, comparing the ratio V₁ /V₂ to a ratio V_H /V_L, and producing an output signal responsive to V₁ /V₂ >

V_H /V_L.

2. A method as in claim 1 including the steps of converting V₁ and V₂ into respective logarithmic values Log₁ and Log₂, converting V_H and V_L into respective logarithmic values Log_H and Log_L, and the step of comparing the ratio V₁ /V₂ to the ratio V_H /V_L is carried out by determining the value X=Log₁ -Log₂ and the value Y=Log_H -Log_L and by determining the difference between the values X and Y, and the step of producing the output signal is carried out responsive to X>

Y.

3. A method as in claim 1 which includes holding one of the light transmitters associated with the first channel at one position which is offset a predetermined distance in a first direction from a given axis to cause the first axis to be squinted, and holding another of the light transmitters associated with the second channel at another position which is offset in a second direction from said given axis to cause the second axis to be squinted.

4. A method as in claim 1 which includes holding one of the light receivers associated with the first channel at one position which is offset from a given axis to cause the first axis to be squinted, and holding another of the light receivers associated with the second channel at another position which is offset from said given axis to cause the second axis to be squinted.

5. A method as in claim 1 which includes directing the light beams in each channel into optical lenses and focusing the light beams through the lenses into light paths, positioning the lens in the first channel at one position which is offset from a given axis and causing the light path in the first channel to be strobed along said squinted first axis and to be received by the light receiver associated with the first channel at an offset distance from the optical center of the light receiver, positioning the lens in the second channel at another position which is offset from said given axis and causing the light path in the second channel to be strobed along said squinted second axis and to be received by the light receiver associated with the second channel at an offset distance from the optical center of the light receiver.

6. A method as in claim 1 which includes directing the light beams through a substantially opaque screen having a plurality of apertures which form field stops for lenses which focus images of respective light beams onto the light receivers, positioning the aperture which forms the field stop associated with the light beam in the first channel at one position which is offset from a given axis sufficient to cause the light path in the first channel to be strobed along said squinted first axis and to be received by the light receiver associated with the first channel along a path which is squinted form the optical center of the light receiver, positioning the aperture which forms the field stop associated with the light beam in the second channel at another position which is offset from said given axis sufficient to cause the light path in the second channel to be strobed along said squinted second axis and to be received by the light receiver associated with the second channel along another path which is squinted from the optical center of the light receiver.

7. A method as in claim 1 which includes the step of controlling the gain of the signals V₁ and V₂ in the ranges V_L <

V₁ <

V_H and V_L <

V₂ <

V_H.

8. A method as in claim 7 which includes the step of establishing a predetermined reference signal V_R where V_L <

V_R <

V_H, and controlling the highest amplitude of the signals V₁ or V₂ ≈

V_R.

9. A method as in claim 8 including the step of establishing V_R in the range of substantially 0.4 dB to 0.8 dB below V_H.

10. A method as in claim 1 in which the optical sensing array is used for safeguarding operating machinery, including the step of stopping operation of the machinery responsive to said output signal.

11. A method as in claim 1 including the step of generating an alarm signal responsive to said output signal.

12. A method as in claim 1 including the step of generating another signal responsive to either V₁ <

V_L or V₂ <

V_L for indicating an unsafe condition of the optical sensing array.

13. An optical sensing array system as in claim 1 in which said first axis is coincident with the optical axis of the light receiving element associated with the first channel and the second axis is displaced laterally from the first axis.

14. An optical sensing array system for controlling the acceptance angle of light beams, the system comprising the combination of a light transmitter having a plurality of light transmitter elements, a light receiver having a plurality of light receiving elements which are arrayed across the optical sensing array from respective ones of the light transmitter elements, means for iteratively strobing light beams from the light transmitter elements in side-by-side channels toward the light receiver elements, beam squinting means for causing the light beam in a first one of the channels to be directed toward the respective light receiving element in the first channel along a first axis which is squinted relative to a second axis along which the light beam in at least a second one of the channels is strobed, means for producing a signal V₁ responsive to light being sensed by the light receiver element of the first channel, means for producing a signal V₂ responsive to light being sensed by the light receiver element of the second channel, means for establishing a predetermined high amplitude value V_H and a predetermined low amplitude value V_L which is below V.sub. H, means for comparing the ratio V₁ /V₂ to the ratio V_H /V_L, and means for producing an output signal responsive to V₁ /V₂ >

V_H /V_L.

15. An optical sensing array system as in claim 14 including means for converting the signals V₁ and V₂ into respective logarithmic values Log₁ and Log₂ and for converting V_H and V_L into respective logarithmic values Log_H and Log_L, and said means for comparing the ratio V₁ /V₂ to the ratio V_H /V_L includes logic means for determining the value X=Log₁ -Log₂ and the value Y=Log_H -Log_L and for determining a difference between X and Y, and said means for producing the output signal responds to said logic means determining that X>

Y.

16. An optical sensing array system as in claim 14 in which said beam squinting means comprises positioning means for holding the light receiver element associated with the first channel at one position which is offset a predetermined distance in a first direction from an optical axis of the light receiving element to cause the first axis to be squinted, said positioning means further holding the light receiver element associated with the second channel at another position which is offset in a second direction from said optical axis to cause the second axis to be squinted.

17. An optical sensing array system as in claim 16 in which said positioning means holds the light receiver elements in spaced-apart relationship along a longitudinal centerline of the light receiver and further holds the adjacent light receiver elements, which are associated with said first and second channels, on opposite sides of said longitudinal centerline.

18. An optical sensing array system as in claim 14 in which said beam squinting means comprises positioning means for holding the light transmitter element associated with the first channel at one position which is offset a predetermined distance in a first direction from an axis of the light receiving element associated with the first channel to cause the first axis to be squinted, said positioning means further holding the light transmitter element associated with the second channel at another position which is offset in a second direction from said optical axis of the light receiving element associated with the second channel to cause the second axis to be squinted.

19. An optical sensing array system as in claim 18 in which said positioning means holds the light transmitter elements in a spaced-apart relationship along a longitudinal centerline of the light transmitter and further holds the adjacent light transmitter elements, which are associated with said first and second channels, on opposite sides of said longitudinal centerline.

20. An optical sensing array system as in claim 14 which includes lens means for focusing the light beams in the channels onto the light receivers, and said beam squinting means includes means for holding the lens means in the first channel at one position which is offset from the optical axis of the light receiving element associated with the second channel for causing the focused light beam in the first channel to be received by the respective light receiver along a squinted axis which is at an offset distance from the optical center of the light receiver, said beam squinting means further including means for holding the lens means in the second channel at another position which is offset from said given axis for causing the focused light beam in the second channel to be received by the light receiver along another squinted axis which is at an offset distance from the optical center of-the light receiver.

21. An optical sensing array system as in claim 14 in which said positioning means includes means for directing the light beams through a substantially opaque screen having apertures which form field stops for lenses which focus images of respective light beams onto the light receivers, said positioning means holding the aperture which forms the field stop associated with the light beam in the first channel at one position which is offset from the optical axis of the light receiving element associated with the first channel sufficient to cause the light path in the first channel to be received by the light receiver associated with the first channel along a path which is squinted from the optical center of the light receiver, said positioning means further holding the aperture which forms the field stop associated with the light beam in the second channel at another position which is offset from the optical axis which is associated with the second channel sufficient to cause the light path in the second channel to be received by the light receiver associated with the second channel along another path which is squinted from the optical center of the light receiver.

22. An optical sensing array system as in claim 14 which includes means for controlling the gain of the signals V₁ and V₂ in the ranges V_L <

V₁ <

V_H and V_L <

V₂ <

V_H.

23. An optical sensing array system as in claim 22 which includes means for establishing a predetermined reference signal amplitude value V_R having the relationship V_L <

V_R <

V_H, and means for controlling the amplitude of the highest signals V₁ or V₂ ≈

V_R.

24. An optical sensing array system as in claim 14 which includes means for generating another signal responsive to either V₁ <

V_L or V₂ <

V_L for indicating an unsafe condition of the optical sensing array.